Doc update to mention Xamarin
Mark TestCases as serializable
Fixed xunit.msbuild to work with paths with white spaces.
Add the ability to specify the shadow copy folder for test runner authors.
Added more extensibility points in TestXxxRunner classes, and fixed up two cases where work was being done in the wrong place.
Code cleanup.
Rename RunSummary to Xunit1RunSummary (to prevent name collisions).
Rename ExecutionTime to ExecutionTimer, and include failures in timing.
Extensibility point overhaul: XunitTestCase and XunitTheoryTestCase.